1. Field of the Invention
The present invention relates to a cylindrical vibration damping device of fluid filled type having a plurality of fluid chambers filled with a non-compressible fluid and intercommunicating through an orifice passage, the device being adapted to provide vibration damping action on the basis of flow action, e.g. the resonance action, of fluid through the orifice passage.
2. Description of the Related Art
In the field of fluid filled type vibration damping devices that utilize vibration damping action based on the flow action of a non-compressible fluid filling the interior, one type of device known to date is a cylindrical vibration damping device of fluid filled type as disclosed for example in U.S. Pat. No. 7,275,738 or in U.S. Unexamined Patent Publication No. US-A-2007273076. In these fluid filled type cylindrical vibration damping devices, an inner shaft fitting and a intermediate sleeve are positioned spaced apart from one another in the diametrical direction and linked by a main rubber elastic body; and an outer tubular member is slipped onto the outside of the intermediate sleeve and affixed fitting thereon. A first and a second pocket portion whose openings are formed through a first and second window portion made in the intermediate sleeve are covered by the outer tubular member, thereby defining a first and a second fluid chamber that are filled with a non-compressible fluid and give rise to relative pressure fluctuations when vibration is input. Further, an orifice passage is formed extending in the circumferential direction between the diametrically opposed faces of the intermediate sleeve and the outer tubular member, with the first and second fluid chamber communicating with one another through this orifice passage. With this design, when vibration is input across the inner shaft fitting and the outer tubular member causing elastic deformation of the main rubber elastic body, the pressure differential arising between the first fluid chamber and the second fluid chamber as a result will produce flow action, e.g. resonance action, of fluid through the orifice passage, thereby creating an orifice effect which is a type of vibration damping effect. Implementation of fluid filled type cylindrical vibration damping devices of this kind as automotive engine mounts, body mounts, diff mounts, suspension mounts and the like is a topic of ongoing research.
In some instances, a fluid filled type cylindrical vibration damping device of the sort described above will be provided with a stopper member attached between the diametrically opposed faces of the inner shaft fitting and the outer tubular member, with the object of preventing excessive displacement of the inner shaft fitting and the outer tubular member in association with input of large-amplitude vibration. The stopper member typically has an arcuate shape extending in the circumferential direction and spanning the first or second window portion between the intermediate sleeve and the outer tubular member, with the circumferentially center section of the stopper member juxtaposed against the outer tubular member, and with the circumferential end portions of the stopper member fitted between the diametrically opposed faces of the outer tubular member and the intermediate sleeve between the first and second window portions in the circumferential direction so that the circumferential center section of the stopper member is attached projecting out towards the inner shaft fitting from the outer tubular member. When excessive vibration is input across the inner shaft fitting and the outer tubular member, the inner shaft fitting and the outer tubular member will come into contact via the intervening stopper member, thereby limiting relative displacement of the two fittings.
In a fluid filled type cylindrical vibration damping device of conventional design equipped with such a stopper member, since the sections where the circumferential ends of the stopper member are attached and supported will overlap the openings of the orifice passage into the fluid chambers, it is difficult to ensure that the orifice passage has an adequate passage cross sectional area and opening area. This has tended to impose limitations on freedom of tuning through appropriate selection of the length and cross sectional area of the orifice passage, resulting in a possible inability to consistently achieve the intended orifice effect.
To cope with this problem, it would be conceivable, for example, to position the circumferential ends of the stopper member at locations away from the diametrically opposed faces of the outer tubular member and the intermediate sleeve between the first and second window portions in the circumferential direction, or to design the stopper member using the inside peripheral section of the outer tubular member. However, considerations such as the stability and ease of assembly of the stopper member with the outer tubular member or intermediate sleeve, the level of strength required of the stopper, and so on make such approaches impractical.